Which IP class should I pick for a network of 50 sites

Class C for the bulk of it, almost certainly, with a small number of higher-tier addresses reserved for the two or three properties where being grouped would actually cost you something. Fifty sites is past the point where the wider tiers can carry the whole estate anyway: only Class C scales that far in a single order.

Start with what each tier can supply

This is the constraint that decides the answer before preference gets a vote. A single Class C order reaches into the hundreds of addresses. Class B tops out in the tens. Class A is a handful. At fifty sites you are already beyond what Class A or Class B can cover alone, so the question is not which tier but what the mix looks like.

A sensible shape for fifty

1. Sort the fifty by consequence. Which of these would genuinely hurt if someone established that they belong to the same operation? For most estates that is a short list, often three or four properties.
2. Put the long tail on Class C. The remaining forty-odd sites get one address each. This is the cheapest per address and the only tier with the supply.
3. Put the short list on a wider tier. Class A or Class B for the few that matter, bought as a separate order on the same account.
4. Leave headroom. Order somewhat more than fifty. Band pricing rewards a single larger order over several small ones, for reasons worked through in Billing and Refunds.

The mistake worth avoiding

The tempting move at this size is to buy the most expensive tier you can afford and treat it as insurance. It is poor value. Fifty sites on the widest available separation still give themselves away instantly if they share a theme, a registrar batch, an analytics identifier or an interlinking pattern no independent publisher would produce. The network layer is one axis and it is the one you can buy; the others cost attention instead.

Spending the difference on making forty sites genuinely distinct at the content and registration level buys more separation than upgrading all fifty a tier.

Practical consequences at this scale

Fifty accounts is where administration starts to matter as much as addressing. A few things worth deciding once rather than fifty times:

• Private nameservers per domain, not one pair reused across the estate.
• A plugin and theme policy you can actually audit, rather than fifty independent drifts.
• Which addresses are held in reserve for sites not yet built, so growth does not mean a new order every fortnight.

If the fifty sites are heavy enough to want their own machine rather than shared accounts, a VPS or dedicated server takes the same address blocks and gives you root. Rates for each tier are on the Class C page and the Class A page; the mechanics of allocation are in IP Diversity.